The proposed research represents an attempt to develop and evaluate a novel pharmaceutical formulation that will provide some degree of tissue specificity in the delivery of anticancer agents to the body. 5- Fluorouracil will be incorporated into human albumin microspheres and formulated for administration as microsuspension with a particle size of about one micron. Such microspheres are cleared from the plasma by the phagocytic activity of cells of the reticulo-endothelial system and certain neoplastic cells. These studies will focus on three distinct areas of investigation. In vitro pharmaceutics studies will examine the incorporation of radiolabeled 5-fluorouracil into albumin microspheres, the rate of desorption and diffusion of drug from the spheres into plasma and the physical-chemical parameters necessary for the production of a satisfactory formultion. Radiotracer techniques will be utilized to study the rate of removal of microspheres containing radiolabeled drug from plasma and their distribution into a variety of tissues in the mouse. Finally, the efficacy of the overall approach will be determined by studying the effectiveness of drug-containing microspheres against several experimental tumors including leukemia L1210 in mice.